Morpholine is excreted in the urine and bile following exposure by any route. The chemical might be expected to be excreted via the renal tubular base transport system, but evidence indicates that this may not be so. Furthermore, although its solubility may be controlled through regulation of urinary pH, its rate of elimination in the urine is not. Studies are continuing to elucidate the renal disposition of this chemical. Preliminary studies indicate that time-varying concentration profiles affect expressions of inhalation toxicity. Rats exposed to a variety of profiles with equal concentration times time, exhibit different degrees of chemical injury to the liver by carbon tetrachloride.